Can I be pregnant and not know it? Hpt are coming back negative. Last period was dec 19th. And im 3 days late

It's unlikely, but. It can be normal for a woman's menstrual cycle to vary in length by a few days from month to month. It sounds like you have had multiple negative home pregnancy tests, which are usually accurate. Just to be sure, you might consider making an appointment with your ob/gyn if your period doesn't come in the next couple days.